1. Field of the Invention
The present invention relates to an organic semiconductor element and the fabrication method thereof.
2. Description of the Related Art
Semiconductors, which are used in a diode, a switch element required in signal processing and a transistor with an amplification function, necessitate physical characteristics such as a high carrier mobility, a low dark current, and a low drive voltage, and so forth. Therefore, an inorganic semiconductor such as silicon is generally used.
Investigations have been conducted into the usage of organic semiconductor elements whose semiconductor layer consists of an organic compound as drive elements for driving electrical elements consisting of organic electroluminescent or other organic materials. Because, in fabrication processes of electrical elements consisting of organic materials and organic semiconductor elements, the number of shared parts is high, there are advantages such that usage of the fabrication devices for the two elements can be shared.
As shown in FIG. 1, a thin film transistor 1 that uses an organic semiconductor thin film (hereinafter referred to as an organic TFT) is laminated, in order from a substrate 2, with a gate electrode 3, and a gate insulation layer 4 that surrounds and insulates the gate electrode 3, and an organic semiconductor layer 5 that acts as a current channel. A source electrode 6 and a drain electrode 7 are provided on the organic semiconductor layer 5. Materials used include Ni and Cr, or similar as the gate electrode 3, an inorganic material such as SiO2 or SiN or a resin such as polymethylmethacrylate (hereinafter referred to as PMMA) as the gate insulation layer 4, and pentacene or similar as the organic semiconductor layer 5.
By changing the electrical potential of the gate electrode of an organic TFT with such a constitution, it is possible to change the thickness of the depletion layer, which is a region in the organic semiconductor layer in which no carriers are present, and the current flowing between the source electrode and drain electrode can be controlled.
Among organic TFTs with the above constitution, a high organic semiconductor carrier mobility has been reported for an organic TFT 1 in which the gate insulation layer 4 is PMMA and the organic semiconductor layer 5 is pentacene, for example, in comparison with an organic TFT in which the gate insulation layer is SiO2.
Reference is to be made to “a lightweight and soft organic transistor changes the appearance of the display”, Nikkei Electronics, Oct. 8, 2001; Vol. 806, Nikkei B P, pp. 55 to 62.
However, it has been ascertained that the organic TFT endurance characteristics are inadequate due to the low insulation strength of PMMA or other organic materials.
The above problem is cited as one example of a problem which the present invention is intended to resolve.